The feature lets you pay to mark a post as "Sponsored" and have it appear prominently in your friends' News Feeds.

Businesses have been able to buy such ads for a while. And ordinary users have always had the option to buy display ads that appear on the right-hand rail of Facebook's website—sometimes using Facebook's targeting to comic effect by targeting coworkers, journalists, or employers. (For a while, "Hire Me" Facebook ads were a thing.)

But ads in the News Feed are generally thought to be the most likely to be noticed, since that's the area of the site where most Facebook users focus their attention.

One thing's for sure: Once Facebook users start noticing these ads, there's almost certainly going to be a ruckus as we sort out the etiquette of advertising aspects of our life to our friends.